The invention relates to an improved composition and method for reducing lost circulation when aqueous or oil base drilling fluids are used.
During oil and gas well drilling operations, it is well known that subterranean formation conditions may be encountered in which substantial amounts, and indeed all, of the drilling fluid may be lost to the formation. This is known in the art as “lost circulation.” In order to overcome the lost circulation, many different materials, known as lost circulation materials/additives, have been added to the drilling fluid to regain full circulation of the drilling fluid.
There is disclosed in co-pending U.S. patent application Ser. No. 10/248,597 filed Jan. 30, 2003, incorporated herein by reference, a method of reducing lost circulation which includes placement of an acidic gellable composition slurry into the location of the wellbore where lost circulation is occurring (the “lost circulation zone”, “thief zone”, etc.) and thereafter contacting the acidic gellable composition slurry with a hardenable alkaline composition slurry whereby the pH of the acidic gellable composition slurry is increased to the extent that the acidic gellable composition slurry is gelled.
The hardenable alkaline composition is a mixture of finely ground paper, diatomaceous earth, micronized cellulose, lime, and optionally but preferably sodium silicate and/or a water soluble sulfate.
This method of overcoming lost circulation has been very successful. However, it has been observed that the mixing time when preparing weighted hardenable alkaline composition slurries is excessive.